Recently, in a manufacturing process of a semiconductor device, a technique called chemical oxide removal (COR) has attracted attention as a micro etching method instead of dry etching or wet etching.
As the COR, there is known a process of etching a silicon oxide film by allowing hydrogen fluoride (HF) gas and ammonia (NH3) gas to adsorb onto a silicon oxide film (SiO2 film) present on the surface of a semiconductor wafer that is an object to be processed in a chamber maintained at a vacuum level, and to react with the silicon oxide film to generate ammonium fluosilicate ((NH4)2SiF6; AFS), and then having the ammonium fluosilicate sublimated by heating in the next step (see, e.g., Japanese Patent Application Publication No. 2005-39185 and Japanese Patent Application Publication No. 2008-160000).
In the case of etching the silicon oxide film as described above, the gaseous mixture of HF gas and NH3 gas is reacted with the silicon oxide film under the conditions that the pressure in the chamber is 10-100 mTorr (1.33-13.3 Pa), the temperature of the semiconductor wafer is 30-40° C., and the flow rate of the total gas is 100-200 sccm (mL/min).